1. Technical Field of the Invention
The present invention relates to an overcurrent interrupting device for interrupting a current when an overcurrent flows into electric circuits mounted on equipment on vehicles, ships, or airplanes.
2. Related Art
Generally, an overcurrent interrupting device, which is installed on an automobile and interrupts an electric current flowing to a load when the electric current is an overcurrent, is known. An intelligent power switch (IPS) having an overcurrent breaking function of interrupting an overcurrent is commercially practical as such an overcurrent interrupting device. The IPS is employed and housed in a junction box as an alternative to a related-art fuse or relay.
Since the IPS has an overcurrent breaking function, the IPS finds a wide range of applications. For example, Japanese Patent publication No. Hei. 10-59090 describes a xe2x80x9cVehicle Power Distribution Devicexe2x80x9d using such an IPS. The vehicle power distribution device detects an overcurrent, an overvoltage, an excessive temperature rise, etc, thereby deactivating an output transistor and interrupting an electric current.
Japanese Patent Publication No. Hei 10-271698 describes a xe2x80x9cVehicle Feeder Systemxe2x80x9d using the IPS. This vehicle feeder system detects an overcurrent, an overvoltage, an excessive temperature rise, etc, thereby interrupting power output from an output circuit.
FIG. 4 shows the general configuration of a related-art overcurrent interrupting device using such an IPS. The overcurrent interrupting device is interposed between a power supply (12V) and a load L. A load switch SW for supplying power to the load L is switched to an ON position, thereby activating the overcurrent interrupting device. An IPS 101 comprises a power MOSFET 110, a boosting and switching circuit 120, a current detection circuit 130, and an overcurrent determination circuit 140.
The power MOSFET 110 is a bulk power transistor. The drain D of the power MOSFET 110 is connected to a power supply (+12V). The source S of the power MOSFET 110 is connected to the load L via the current detection circuit 130, and the gate G of the power MOSFET 110 is connected to the boosting and switching circuit 120.
When the load switch SW is turned on, the boosting and switching circuit 120 outputs a pulse signal which is turned on/off at a predetermined duty cycle. The pulse signal generated by the boosting and switching circuit 120 is supplied as a gate signal to the gate G of the power MOSFET 110.
The current detection circuit 130 detects the magnitude of an electric current flowing from the source S of the power MOSFET 110 to the load L, and outputs the result of detection as a current value. The current value output from the current detection circuit 130 is supplied to the overcurrent determination circuit 140. The overcurrent determination circuit 140 compares the current value output from the current detection circuit 130 with a predetermined value stored beforehand in the overcurrent determination circuit 140. If the current value output from the current detection circuit 130 is greater than the determination value, an overcurrent detection signal to this effect is supplied to the boosting and switching circuit 120.
The operation of the related-art overcurrent interrupting device having the foregoing configuration will now be described. When the load switch SW is in an OFF state, the boosting and switching circuit 120 outputs a low-level signal (hereinafter called an xe2x80x9cL-level signalxe2x80x9d) Accordingly, the power MOSFET 110 is held in an OFF state, and no current flows to the load L. When the load switch SW is turned on in this state, the boosting and switching circuit 120 outputs a pulse signal and supplies the signal to the gate G of the power MOSFET 110 as a gate signal. As a result, the power MOSFET 110 is turned on/off in accordance with the gate signal, thereby intermittently supplying an electric current to the load L.
The current detection circuit 130 detects the magnitude of an electric current flowing from the power supply to the load L via the power MOSFET 110 at all the time, and supplies the result of detection to the overcurrent determination circuit 140. The overcurrent determination circuit 140 compares the current value output from the current detection circuit 130 with the predetermined value stored in the overcurrent determination circuit 140. When the current value detected by the current detection circuit 130 is greater than the determination value, an overcurrent detection signal to this effect is supplied to the boosting and switching circuit 120. The boosting and switching circuit 120 suspends an output of a pulse signal and outputs a low-level signal. Consequently, the power MOSFET 110 enters an OFF state, thereby interrupting an electric current flowing to the load L.
As mentioned above, the IPS 101 used in the related-art overcurrent interrupting device compares the current value detected by the current detection circuit 130 with the determination value stored in the overcurrent determination circuit 140, thereby determining whether or not the detected current is an overcurrent.
Whether the detected current is an overcurrent is determined depending on the basis of a load. The determination value stored in the overcurrent determination circuit 140 of the IPS is only a fixed value. Hence, an IPS of one type cannot be shared among a plurality of types of loads, and hence it is necessary to use the several types of IPSs each having suitable determination value for each load. Consequently, in relation to a vehicle equipped with a plurality of types of loads, the number of types of overcurrent interrupting devices to be used is increased. This also results in an increase in the number of types of electronic control units (ECUs) equipped with overcurrent interrupting devices.
The present invention has been conceived to solve such a problem and is aimed at providing an overcurrent interrupting device which can be shared among a plurality of types of loads.
To achieve the object, the present invention provides, according to the first aspect of the invention, an overcurrent interrupting device comprising:
a semiconductor switch which controls an electric current flowing from a power supply to a load;
a current detection circuit which detects a current value of an electric current flowing from the semiconductor switch to the load;
a determination value selection circuit which selects a determination value for determining a overcurrent;
an overcurrent determination circuit which determines whether or not the current flowing from the semiconductor switch to the load is an overcurrent, on the basis of the current value and the determination value selected by the determination value selection circuit, and outputs a result of the determination; and
a control circuit which controls the semiconductor switch on the basis of the result of the determination.
According to the first aspect, a determination value selection circuit enables selection of a determination value used for determining occurrence of an overcurrent. Accordingly, there can be provided an overcurrent interrupting device capable of being shared among loads of different types which enable flow of different currents. Consequently, the general versatility of the overcurrent interrupting device is improved, thereby diminishing the number of types of ECUs equipped with the overcurrent interrupting device.
According to a second aspect of the invention, in the overcurrent interrupting device of the first aspect, a plurality of switches are connected to the determination value selection circuit, and the determination value selection circuit selects the determination value in accordance with a setting state of the plurality of switches.
According to the second aspect, a plurality of switches are set in accordance with an electric current which can be caused to flow through a load. A determination value compliant with a load is selected by means of a determination value selection circuit. Hence, there can be provided an overcurrent interrupting device having superior versatility despite having a simple structure.
According to a third aspect of the invention, in the overcurrent interrupting device of the first aspect, a CPU is connected to the determination value selection circuit, and the determination value selection circuit selects the determination value in accordance with a signal output from the CPU.
According to the third aspect, a CPU supplies a predetermined signal to a determination value selection circuit in accordance with an electric current which can be caused to flow through a load. A determination value compliant with the load is selected. Hence, an overcurrent interrupting device having superior versatility can be provided. In this case, the CPU can double as a CPU provided on equipment to which the overcurrent interrupting device is applied. By means of such a configuration of the overcurrent interrupting device, the configuration of the overcurrent interrupting device can be simplified much further.
To achieve the object, the present invention provides, according to a fourth aspect of the invention, a interrupting device comprising:
a semiconductor switch which controls an electric current flowing from a power supply to a load;
a detector which detects a condition of the load;
a determination value selection circuit which selects a determination value for determining an abnormal condition of the load;
a determination circuit which determines whether or not the load is in the abnormal condition on the basis of the condition of the load and the determination value selected by the determination value selection circuit, and outputs a result of the determination; and
a control circuit which controls the semiconductor switch on the basis of the result of the determination.
According to the fourth aspect, a determination value selection circuit enables selection of a determination value used for determining occurrence of abnormal condition of the load. Accordingly, there can be provided an interrupting device capable of being shared among loads of different types which enable flow of different currents. Consequently, the general versatility of the interrupting device is improved, thereby diminishing the number of types of ECUs equipped with the interrupting device.
According to a fifth aspect of the invention, in the interrupting device of the fourth aspect, the condition of the load includes one of a current condition, a voltage condition and a temperature condition of the load, and the abnormal condition includes one of an overcurrent condition, an overvoltage condition and an excessive temperature rise condition.
According to a sixth aspect of the invention, in the interrupting device of the fourth aspect,
a plurality of switches are connected to the determination value selection circuit, and the determination value selection circuit selects the determination value in accordance with a setting state of the plurality of switches.
According to a seventh aspect of the invention, in the interrupting device of the fourth aspect, a CPU is connected to the determination value selection circuit, and the determination value selection circuit selects the determination value in accordance with a signal output from the CPU.